1. Field of the Invention
This invention relates broadly to a method and apparatus for pouring ingots, and more particularly for pouring hot top ingots by weight instead of volume.
2. Description of the Prior Art
In the production of steel ingots, for example, ingots are ordered according to metallurgical grade, weight and size. Generally, depending on metallurgical grade, the teeming practice uses one of three types of ingot molds. Hot metal is poured into either a bottle cap ingot mold of fixed volume, or either an open-top or hot-top ingot mold of variable volume. A similar teeming practice is used in other metal industries.
An improvement in teeming practice occurred recently when a teeming ladle having a weight-loss weigher system was used to pour open top ingots by ordered weight rather than by volume. However, when using this practice on hot top ingot molds, the ingot mold body was poured by weight, but the ingot hot top was still poured by volume to a mark in the hot top casting. This was because of the unavailability of a weigher system to do otherwise. Using the recent practice, only the correct ingot body weight was achieved. Only a theoretically correct hot top addition was made, this being based on volume and not weight, with the expectation of providing enough liquid steel to fill the shrinkage cavity in the ingot mold body as the metal freezes.
There are some sources of considerable errors when using the volume-based teeming practice, regardless of whether an operator pours hot metal into ingot bodies alone, or into open-top or hot-top ingot molds. In any production operation where ingot molds are reused, ingot mold volume changes due to mold and/or stool wear. This causes a corresponding change in apparent mold body volume and carries over to a hot top volume variation. Further, when teeming to a mark in the ingot hot top casting, which is difficult for a pouring operator to see, the steel volume added to the ingot hot top is another source of volume error.
In order to compensate for these volume errors and insure that metallurgically sound steel will exist in the ingot mold body, it generally is the practice of pouring operators to add extra steel to the ingot hot top. In primary mills that follow pouring, the ingot is rolled and the top portion is cropped and scrapped. It has been discovered that the weight of scrapped ingot tops poured by the volume pouring method varies from slightly less than 10% to greater than 15% of ingot body weight. This variation is attributed to one or more sources of error caused by ingot mold/stool size wear, variable hot top allowances and the inability of the pouring operator to stop hot metal flow into the ingot at the correct height.